When Susan and Matt Carroll moved to Ashburn, they had decided, like many young couples buying a home, that they would be happy to send children to what they thought was their neighborhood school.

But by the time they had their first baby in 2004, they learned that nearby Mill Run Elementary wouldn’t be their school. And by the time their oldest son, Turner, starts fourth grade this fall, he already will have had to switch schools three times.

“There are a lot of people who are not happy,” Susan Carroll said. Even if parents believe, as Carroll does, that the quality of Loudoun County’s schools overall is consistently good, she said, “it’s very hard not to react with emotion. This is so personal, where your kids go to school and how you plan your life around it.”

With staggering growth rates in much of Northern Virginia, change is the new constant. In Loudoun County, population shot up 84 percent from 2000 to 2010. The Weldon Cooper Center for Public Service at the University of Virginia estimates Loudoun’s population has risen another 7 percent in the past two years, according to numbers scheduled for release Friday.

There was a time when everyone knew which high school kids in each corner of the county would attend, which football team they would cheer for on Friday nights. That was before the county was adding 2,500 to 3,500 new students — the size of an average U.S. school system or more — every year. School boundaries used to carve into counties as though into granite, helping to define communities’ identities and traditions over time. Now they’re more like an Etch a Sketch, constantly getting shaken up, erased, redrawn.

Those lines on the map matter to many parents, affecting two of the things they care about most: their children and, for many, their biggest financial stake, their house.

“People buy homes thinking they will be attending that particular school through the life span of that household,” said Ajay Rawat, coordinator of facilities planning services in Fairfax County Public Schools. But in many parts of the region, that’s no longer a safe bet; parents can’t count on moving into the neighborhood near the school with the particular attention to autistic students or the Spanish immersion track or the technology magnet program.

And so just about every redistricting plan sparks a battle. People scrutinize the lines and talk to neighbors. They send e-mails — 100 to 200 every day, one Loudoun board member said. They question engineering studies and linear regression models of population growth. They wear school colors and crowd into public hearings — more than 2,000 at a single meeting in Fairfax several years ago.

They accuse school officials of racism. They demand documents through the federal open-records law, hoping to prove errors and conspiracies. They file lawsuits, as parents did unsuccessfully in Loudoun County last year, to try to stop the changes.

Sometimes they win concessions, persuade officials to tweak plans.

And sometimes they throw their hands up, with an all-caps message like William Johnson wrote at the end of a long and detailed e-mail to county leaders in Arlington this fall:

For school officials, there’s an awful lot at stake, too. In many cases, they’re trying to alleviate or prevent badly overcrowded schools, hoping to improve students’ experiences and performance with smaller classes, more individualized attention and better access to resources such as computers and science labs. They’re often trying to increase or maintain diversity, whether for cultural or for academic reasons or both. They want to minimize costs and increase efficiency. They think about existing dividing lines, such as rivers and freeways and housing developments. They try to ensure safety, not asking children to walk across busy roads to get to school. And they want to avoid splintering communities.

But as they find with each redistricting battle, the ways that people define communities now are increasingly complex.

The District, which has been steadily losing students, is about to launch its first major redistricting in decades, and Charles and Prince George’s counties in Maryland are considering shifts.

In Arlington, anticipating a shortfall of more than 2,000 seats in elementary schools by 2017 (and they already have more than 100 trailers), school officials are planning two new schools and three expansions over six years. Along with surveys and more than 125 community meetings over the past five months, Arlington Public Schools leaders offered a do-it-yourself boundaries map and say they will consider public efforts to craft solutions.

Some residents question Arlington’s projections. William Johnson thinks enrollment won’t grow so quickly and thinks the county could be wasting millions of taxpayer dollars to build new schools. Sociologist Fred Millar says the county’s plans are all wrong for a completely different reason: He believes their efforts to keep neighborhoods together (something most parents support) has created a system in which some schools have more minority and low-income students than others, perhaps perpetuating academic achievement gaps.

And many parents just don’t want to uproot their kids.

“We’re trying to engage the community as much as possible because we do understand boundary moves are difficult,” said Meg Tuccillo, the interim director of facilities planning for Arlington schools. “Families become personally connected and committed to the schools that they’re in.”

Projecting population change is complicated. School officials analyze birth rates, housing starts, current enrollment and a host of other factors. In Fairfax, administrators didn’t anticipate a recent large influx of immigrants with larger families or a bump in enrollment after the economic crash that they think came from parents no longer able to afford private-school tuition. In Loudoun, when building stopped after the crash, they were amazed that they were still seeing more than 2,000 new students a year.

Even when they almost nail it — the projection came within 26 kids countywide one year in Loudoun — there are still bumps and dips at individual schools that throw things off.

And so they keep adjusting.

“It’s like a Rubik’s Cube,” Carroll said.

Growing pains

Many school divisions in the area are rejiggering their borders now, or at least looking at the possibility.

Montgomery County Public Schools, which is growing by 2,500 students a year, is not undergoing boundary changes now but is beginning to study ways to relieve anticipated overcrowding in part of the county.

On Thursday night, Alexandria City Public Schools Superintendent Morton Sherman told the board that it’s time they begin talking about boundary changes. “That’s a euphemism,” he said afterward, “instead of redistricting — the R-word.” Enrollment has increased more than 20 percent over the past four years, and they’re projecting another 7 percent bump next year.

In Prince William County, the public schools continue to grow by about 2,000 or so students a year. What that means, said Dave Cline, an associate superintendent, “is every year you need a new high school, or one-and-a-half middle schools, or two new elementary schools.”

The school board is always trying to avoid situations that force families to switch to a new school and then, two years later, face another change, said Prince William County School Board member Steven Keen. “But we always hear from parents concerned about that. . . . Along the Linton Hall corridor, you see a lot of that.”

On Thursday night, the Fairfax County School Board approved a plan to build three new elementary schools and a new high school by 2018; the district has been growing by about 3,000 students a year for the last several years.

Change is hard, Rawat said, and schools officials hear that loud and clear. “But at the end of the day, after everything settles down, generally people are okay,” Rawat said. For the most part, people like their new schools.

“Or we go on to the next boundary study,” said Denise James, director of facilities planning in Fairfax, “and something even more controversial comes up.”

In Loudoun, administrator Sam Adamo has seen the system grow from 22,000 students when he started in 1997 to almost 70,000 today.

“When you have that kind of growth and you’re opening new schools . . . it creates a lot of angst,” Adamo said. “Particularly in growth areas, you’re constantly moving students, and schools become overcrowded, you construct a new one, and need to establish attendance areas so some kids are moving and some kids stay. You create a lot of turmoil in the community.”

Two new schools slated to open in the fall made officials look at 11 elementary schools, with about 11,000 children potentially affected by changes before they made their final decision.

On Tuesday, the Loudoun school board passed a measure that will allow parents to switch their children to schools outside of their attendance zones if the schools are under-enrolled and parents provide transportation. Proponents think it could ease concerns by giving parents more options. Board member Jennifer Bergel, who voted against it, said she doesn’t think such switches are an answer to boundary changes because if under-enrolled schools swell, the following year, the students might have to return to their original schools.

“Realistically, it could be pretty disruptive,” Bergel said.

More growth predicted

In Belmont Glen, the problem is not just the long drive to Turner Carroll’s latest elementary school, past a couple other elementary schools. It’s not just the pervasive sense that Creighton’s Corner Elementary is, as the PTA president says, “a bit of an overflow school,” with an ever-shifting group of students.

It’s not just the hours and money parents put into fundraising for the playground and library of a new school that they were then asked to leave. And it’s not just that the latest school is already overcrowded, with nearly 1,200 students jammed in — so many that some of their neighbors’ children were sent to Mill Run as “overflow” students.

“We moved here to raise our family,” said Kim Maresca, a neighbor of the Carrolls’. “When I moved in, I had no idea there would be so much change — I never fathomed this could happen.”

They keep asking, “When is this going to stop?”

The answer, for much of Northern Virginia, is: not any time soon.

In Loudoun County, U-Va.’s Cooper Center projects that growth will slow, but still, from 2010 to 2040, the population will grow by another 81 percent. And it’s a young county, with almost a third of the population younger than 20.

“I do feel for them” in Belmont Glen, said school board member Brenda Sheridan. “I think stabilizing them is really important.”

But as much as school board members want to keep neighborhoods together when they can, Sheridan said, they need to find the best solution for the entire district.

Some parents in Belmont Glen have given up. Some, like Susan Carroll and Maresca, were appreciative that the board is able to alleviate overcrowding with bright new schools and that board members heard their plea this time: If you have to move our kids, send them back to a school that’s closer, one that was our neighborhood school a few years ago. In December, the board adopted a plan that doesn’t send them to another new school; next year, Belmont Glen kids will be at Hillside Elementary again.

For now, at least.

The new school is projected to be overcrowded in a couple of years. And there’s another new elementary school planned nearby.

“We’re still moving,” Carroll said, believing her sons will be bounced to yet another school soon.